This invention relates to an apparatus for protecting a rotating machine such as an electric motor, internal combustion engine or other drive means and/or driven equipment such as centrifugal compressors, fans, pumps, conveyors, and the like, in the event such a machine goes into reverse rotation and, in particular to an apparatus connected to the oil pump that will automatically supply lubrication to the machine's lubricated components with the oil pump rotating in either normal or reverse direction.
Machines such as centrifugal compressors are able to operate as turbines which, unfortunately, is typically what occurs when there is a check valve failure. Conventionally, the oil pump is coupled directly to the compressor drive motor and will attempt to pull oil out of the compressor bearings and other lubricated components when the machine experiences a reversal in rotation. This, of course, can lead to damage to the bearings and other machine parts.
One prior method of providing reverse rotation protection is to provide an independently driven auxiliary pump which takes over the lubrication load if the primary pump fails or the machine is turning backwards, but unfortunately reverse rotation often occurs when there is a power failure that renders such auxiliary pumps inoperative.
Another prior method of providing reverse rotation protection is to provide a by-pass system utilizing four check valves to insure that oil is delivered to the machine from the primary pump regardless of the direction of rotation of the machine shaft. Such a system has numerous components and connections which both increase the likelihood of leaks and increases the cost of the system. Further, the swing type check valves often used normally oscillate slightly during service, sometimes leading to wear and eventual failure of the pivot and therefore the valve.
U.S. Pat. No. 5,199,528 , describes a flow controller for protecting a rotating machine that works quite well in practice. However, it has been found that under certain conditions it is possible for contamination in the oil to find its way between the valve shuttle and the controller housing, which might hinder the operation of the device. Additionally, the thermal expansion of different coacting material parts or transient temperature conditions may, on occasion create adverse operating conditions. These problems can be alleviated by increasing the gap between the shuttle and the housing, but this may lead to unwanted oil leakage decreasing the amount of oil available for lubrication. The prior art device relies on free floating balls to selectively open and close ports in response to the direction of oil flow. Significant flow is required to lift the balls into their seats.
Protective devices in the prior art have provided a margin of safety, but the protective equipment itself can fail thereby endangering the machine.